1. Field of the Invention
The invention is directed to an improved fuel injection valve for internal combustion engines.
2. Description of the Prior Art
One fuel injection valve known for instance from published, nonexamined German patent application DE 41 15 477 A1 includes an outer valve needle and an inner valve needle guided in it are located in a housing. Both valve needles cooperate, by their end toward the combustion chamber, with a valve seat face in which there are two rows of injection openings. The outer row of injection openings is controlled by the outer valve needle, and the inner row of injection openings is correspondingly controlled by the inner valve needle. Through a high-pressure conduit embodied in the housing, the injection openings are supplied with fuel at high pressure, which emerges, controlled by the valve needles, through the injection openings and from there is injected into the combustion chamber of the engine.
A control chamber is embodied in the housing of the fuel injection valve, and its pressure acts on the face end of a pressure piston which is connected to the inner valve needle. In this way, via the pressure in the control chamber, a closing force on the inner valve needle is produced, which keeps this valve needle in contact with the valve seat face. The control chamber can communicate with the injection pressure via a control valve, or can be relieved into a leak fuel chamber, so that the pressure in the control chamber can be controlled in this way. The opening pressure on the inner and outer valve needles is generated, in this known valve by the imposition of fuel pressure on a pressure face, embodied on each of the valve needles; the pressure at which the valve needles open is called the opening pressure.
The known fuel injection valve has the disadvantage, however, that the closing force on the outer valve needle is not generated hydraulically but rather via a fixedly prestressed closing spring. The opening pressure of the outer valve needle is therefore not regulatable, and it can be injected through the outer row of injection openings only at a minimum pressure equivalent to the opening pressure of the outer valve needle. Moreover, the prior art has the disadvantage that the control valve that regulates the pressure in the control chamber is embodied as a 3/2-way valve with a slide seat, so that it is relatively complicated and hence expensive to produce. It is thus not possible in the known fuel injection valve to control the injection cross section arbitrarily.